1. Field of the Invention
The present invention relates broadly to the field of printing apparatus and more specifically to the field of non-impact offset printing apparatus wherein cut sheet paper is fed to a rotatable drum type printing apparatus for accurate registration of the margins of the printed matter on each sheet.
2. Description of the Prior Art
In a non-impact printer of the offset type, it is necessary to accurately and repeatably match up the paper to its intended image so that when the image is affixed to the page the proper margins are achieved. A mechanism for providing this makes for repeatable registration of printed matter in the direction of paper travel assuming proper registration transverse to the paper's motion is achieved by some other means as for example, edge guides or guide walls, etc.
In a compact non-impact printer it is possible for the image to be placed on the offset medium (drum or belt) before a sheet of paper is ever fed. Therefore, it is possible for feed and transport error to affect registration. The motion of the paper must be "recalibrated" so that the page will meet up with its intended image. To provide this recalibration, registration fingers or an interposer become a necessary adjunct to the printing apparatus.
There are several requirements that such a mechanism should fulfill. The mechanism should not take an inordinate amount of space. Its location should be as close as possible to the transfer location. It should be relatively inexpensive and reliable to maintain and operate. It should be mechanically linked (i.e. through timing belts) to the offset medium for highest accuracy. Its motion should provide the proper transition from paper path speed to transfer speed. It should be a cyclic device with a frequency of one actuation per registered sheet of paper. A number of registration methods are possible that attempt to solve this task. However, they all fall short in one or more of the above requirements.
For example, rotating fingers are simple, but they take up too much space and they do not provide the ideal transition motion that is required for smooth operation of the device. A belt with fingers attached would work, but belts are relatively expensive.